As wiring materials for electronic devices such as flat display panels including plasma displays, liquid crystal displays, semiconductor elements including LSI and solar cell panels, silver and copper metal wiring materials have been used. When heat treatment at a high temperature such as 600 to 700° C. is required during manufacturing devices such as plasma display panels, liquid crystal displays and solar cell panels of the above electronic devices, silver wiring materials have been used because the materials are not oxidized in the high temperature heat treatment and keep high electrical conductivity.
In recent years, cyclic utilization of global resources have been demanded to lead a movement for suppressing use of the noble metal materials. In order to realize a low cost of electronic devices, use of copper, which is plenty of resource, has been studied. However, since highly pure copper easily tends to be oxidized to have high electric resistance when oxygen enters the high temperature heat treatment process, a function for wiring material will be lost. There have been reported technologies for improving resistance to oxidation of the copper material by adding a secondary element such as aluminum, titanium, gold, silver, nickel, molybdenum, etc to copper.
As disclosed in patent document Nos. 1, 2 and 3, there are proposed structures wherein copper wires are covered with copper film containing aluminum in order to suppress oxidation of copper wiring of electronic circuits such as LSI during a heat treatment at around 400° C.
However, if these elements are added to copper, points where additive elements are present become centers of scattering of electrons so that electrical resistivity increases. Accordingly, high oxidizing resistance and low electrical resistivity are not contradict to each other and hard to coexist.
Even if the copper wires are covered with materials containing materials with resistance to oxidation, it was impossible to suppress oxidation at the time of heat treatment at high temperatures such as 600 to 700° C. when a thickness or a composition thereof is insufficient,
Patent document 1: Japanese Patent Laid-open S62-290150
Patent document 1: Japanese Patent Laid-open H05-102155
Patent document 1: Japanese Patent Laid-open 2007-188982